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Add a bunch more documentation (and rewrite README) (#86)
## Summary: In this commit, I add a bunch more documentation of how to use genqlient, including a getting started guide, and a FAQ that also acts as a how-to shaped index of common configuration options and extension points. Much of this is adapted from the internal doc I wrote at Khan, or reorganized from what was in the README. Speaking of which, now that there are better places for all the details, I rewrote the README to be a bit more of an overview and index of other documentation. (For now I left the "unmaintained" notes, which I'll remove fairly soon once all our ducks are in a row.) Fixes #26, #39. Issue: #26 Issue: #39 ## Test plan: make check, read the docs Author: benjaminjkraft Reviewers: mahtabsabet, benjaminjkraft, aberkan, dnerdy, jvoll, MiguelCastillo Required Reviewers: Approved By: mahtabsabet Checks: ✅ Test (1.17), ✅ Test (1.16), ✅ Test (1.15), ✅ Test (1.14), ✅ Lint, ✅ Test (1.17), ✅ Test (1.16), ✅ Test (1.15), ✅ Test (1.14), ✅ Lint Pull Request URL: #86
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| # Frequently Asked Questions | ||
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| This document describes common questions about genqlient, and provides an index to how to represent common query structures. For a full list of configuration options, see [genqlient.yaml](genqlient.yaml) and [genqlient_directive.graphql](genqlient_directive.graphql). | ||
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| ## How do I set up genqlient to … | ||
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| ### … get started? | ||
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| There's a [doc for that](INTRODUCTION.md)! | ||
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| ### … use an API that requires authentication? | ||
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| When you call `graphql.NewClient`, pass in an HTTP client that adds whatever authentication headers you need (typically by wrapping the client's `Transport`). For example: | ||
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| ```go | ||
| type authedTransport struct { | ||
| wrapped http.RoundTripper | ||
| } | ||
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| func (t *authedTransport) RoundTrip(req *http.Request) (*http.Response, error) { | ||
| key := ... | ||
| req.Header.Set("Authorization", "bearer "+key) | ||
| return t.wrapped.RoundTrip(req) | ||
| } | ||
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| func MakeQuery(...) { | ||
| client := graphql.NewClient("https://api.github.com/graphql", | ||
| &http.Client{Transport: &authedTransport{wrapped: http.DefaultTransport}}) | ||
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| resp, err := MyQuery(ctx, client, ...) | ||
| } | ||
| ``` | ||
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| For more on wrapping HTTP clients, see [this post](https://dev.to/stevenacoffman/tripperwares-http-client-middleware-chaining-roundtrippers-3o00). | ||
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| ### … make requests against a mock server, for tests? | ||
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| Testing code that uses genqlient typically involves passing in a special HTTP client that does what you want, similar to authentication. For example, you might write a client whose `RoundTrip` returns a fixed response, constructed with [`httptest`](https://pkg.go.dev/net/http/httptest). Or, you can use `httptest` to start up a temporary server, and point genqlient at that. Many third-party packages provide support for this sort of thing; genqlient should work with any HTTP-level mocking that can expose a regular `http.Client`. | ||
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| ### … test my GraphQL APIs? | ||
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| If you want, you can use genqlient to test your GraphQL APIs; as with mocking you can point genqlient at anything that exposes an ordinary HTTP endpoint or a custom `http.Client`. However, at Khan Academy we've found that genqlient usually isn't the best client for testing; we prefer to use a lightweight (and weakly-typed) client for that, and may separately open-source ours in the future. | ||
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| ### … handle GraphQL errors? | ||
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| Each genqlient-generated helper function returns two results, a pointer to a response-struct, and an error. The response-struct will always be initialized (never nil), even on error. If the request returns a valid GraphQL response containing errors, the returned error will be [`As`-able](https://pkg.go.dev/errors#As) as [`gqlerror.List`](https://pkg.go.dev/github.com/vektah/gqlparser/v2/gqlerror#List), and the struct may be partly-populated (if one field failed but another was computed successfully). If the request fails entirely, the error will be another error (e.g. a [`*url.Error`](https://pkg.go.dev/net/url#Error)), and the response will be blank (but still non-nil). | ||
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| For example, you might do one of the following: | ||
| ```go | ||
| // return both error and field: | ||
| resp, err := GetUser(...) | ||
| return resp.User.Name, err | ||
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| // handle different errors differently: | ||
| resp, err := GetUser(...) | ||
| var errList *gqlerror.List | ||
| if errors.As(err, &errList) { | ||
| for _, err := range errList { | ||
| fmt.Printf("%v at %v\n", err.Message, err.Path) | ||
| } | ||
| fmt.Printf("partial response: %v\n", resp) | ||
| } else if err != nil { | ||
| fmt.Printf("http/network error: %v\n", err) | ||
| } else { | ||
| fmt.Printf("successful response: %v\n", resp) | ||
| } | ||
| ``` | ||
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| ### … require 32-bit integers? | ||
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| The GraphQL spec officially defines the `Int` type to be a [signed 32-bit integer](https://spec.graphql.org/draft/#sec-Int). GraphQL clients and servers vary wildly in their enforcement of this; for example: | ||
| - [Apollo Server](https://github.com/apollographql/apollo-server/) explicitly checks that integers are at most 32 bits | ||
| - [gqlgen](https://github.com/99designs/gqlgen) by default allows any integer that fits in `int` (i.e. 64 bits on most platforms) | ||
| - [Apollo Client](https://github.com/apollographql/apollo-client) doesn't check (but implicitly is limited to 53 bits by JavaScript) | ||
| - [shurcooL/graphql](https://github.com/shurcooL/graphql) requires integers be passed as a `graphql.Int`, defined to be an `int32` | ||
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| By default, genqlient maps GraphQL `Int`s to Go's `int`, meaning that on 64 bit systems there's no client-side restriction. If you prefer to limit integers to `int32`, you can set a binding in your `genqlient.yaml`: | ||
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| ```yaml | ||
| bindings: | ||
| Int: | ||
| type: int32 | ||
| ``` | ||
| Or, you can bind it to any other type, perhaps one with size-checked constructors; see the [`genqlient.yaml` documentation](`genqlient.yaml`) for more details. | ||
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| ## How do I make a query with … | ||
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| ### … a specific name for a field? | ||
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| genqlient supports GraphQL field-aliases, and uses them to determine the Go struct field name. For example, if you do | ||
| ```graphql | ||
| query MyQuery { | ||
| myGreatName: myString | ||
| } | ||
| ``` | ||
| and genqlient will generate a Go field `MyGreatName string`. Note that the alias will always be uppercased, to ensure the field is visible to the Go JSON library. | ||
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| ### … nullable fields? | ||
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| There are two ways to handle nullable fields in genqlient. One way is to use the Go idiom, where null gets mapped to the zero value; this is the default in genqlient. So if you have a GraphQL field of type `String`, and you do: | ||
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| ```graphql | ||
| query MyQuery(arg: String) { | ||
| myString | ||
| } | ||
| ``` | ||
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| then genqlient will generate a Go field `MyString string`, and set it to the empty string if the server returns null. This works even for structs: if an object type in GraphQL is null, genqlient will set the corresponding struct to its zero value. It can be helpful to request `id` in such cases, since that’s a field that should always be set, or `__typename` which is guaranteed to be set, so you can use its presence to decide whether to look at the other fields. | ||
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| For input fields, you often want to tell genqlient to send null to the server if the argument is set to the zero value, similar to the JSON `omitempty` tag. In this case, you can do: | ||
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| ```graphql | ||
| query MyQuery( | ||
| # @genqlient(omitempty: true) | ||
| arg: String, | ||
| ) { | ||
| myString | ||
| } | ||
| ``` | ||
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| You can also put the `# @genqlient(omitempty: true)` on the first line, which will apply it to all arguments in the query. | ||
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| If you need to distinguish null from the empty string (or generally from the Go zero value of your type), you can tell genqlient to use a pointer for the field or argument like this: | ||
| ```graphql | ||
| query MyQuery( | ||
| # @genqlient(pointer: true) | ||
| arg: String, | ||
| ) { | ||
| # @genqlient(pointer: true) | ||
| myString | ||
| } | ||
| ``` | ||
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| This will generate a Go field `MyString *string`, and set it to `nil` if the server returns null (and in reverse for arguments). Such fields can be harder to work with in Go, but allow a clear distinction between null and the Go zero value. Again, you can put the directive on the first line to apply it to everything in the query, although this usually gets cumbersome. | ||
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| See [genqlient_directive.graphql](genqlient_directive.graphql) for complete documentation on these options. | ||
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| ### … GraphQL interfaces? | ||
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| If you request an interface field, genqlient generates an interface type corresponding to the GraphQL interface, and several struct types corresponding to its implementations. For example, given a query: | ||
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| ```graphql | ||
| query GetBooks { | ||
| favorite { | ||
| title | ||
| ... on Novel { | ||
| protagonist | ||
| } | ||
| ... on Dictionary { | ||
| language | ||
| } | ||
| } | ||
| } | ||
| ``` | ||
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| genqlient will generate the following types (see [below](#-genqlient-generate-such-complicated-type-names) for more on the names): | ||
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| ```go | ||
| type GetBooksFavoriteBook interface { | ||
| GetTitle() string | ||
| } | ||
| type GetBooksFavoriteNovel struct { | ||
| Title string | ||
| Protagonist string | ||
| } | ||
| type GetBooksFavoriteDictionary struct { | ||
| Title string | ||
| Language string | ||
| } | ||
| // (similarly for any other types that implement Book) | ||
| ``` | ||
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| These can be used in the ordinary Go ways: to access shared fields, use the interface methods; to access type-specific fields, use a type switch: | ||
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| ```go | ||
| resp, err := GetBooks(...) | ||
| fmt.Println("Favorite book:", resp.Favorite.GetTitle()) | ||
| if novel, ok := resp.Favorite.(*GetBooksFavoriteNovel); ok { | ||
| fmt.Println("Protagonist:", novel.Protagonist) | ||
| } | ||
| ``` | ||
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| The interface-type's GoDoc will include a list of its implementations, for your convenience. | ||
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| ### … documentation on the output types? | ||
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| For any GraphQL types or fields with documentation in the GraphQL schema, genqlient automatically includes that documentation in the generated code's GoDoc. To add additional information to genqlient entrypoints, you can put comments in the GraphQL source: | ||
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| ```graphql | ||
| # This query gets the current user. | ||
| # | ||
| # If you also need to specify options on the query, you can put | ||
| # the @genqlient directive after the docuentation, like this: | ||
| # | ||
| # @genqlient(omitempty: true) | ||
| query GetUser { ... } | ||
| ``` | ||
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| ## Why does… | ||
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| ### … genqlient generate such complicated type-names? | ||
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| The short answer is that GraphQL forces our hand. For example, consider a query | ||
| ```graphql | ||
| query GetFamilyNames { | ||
| user { | ||
| name | ||
| children { | ||
| name | ||
| } | ||
| } | ||
| } | ||
| ``` | ||
| which returns the following JSON: | ||
| ```graphql | ||
| { | ||
| "user": { | ||
| "name": "Ellis Marsalis Jr.", | ||
| "children": [ | ||
| {"name": "Branford Marsalis"}, | ||
| {"name": "Delfeayo Marsalis"}, | ||
| {"name": "Jason Marsalis"}, | ||
| {"name": "Wynton Marsalis"} | ||
| ] | ||
| } | ||
| } | ||
| ``` | ||
| We need two different `User` types to represent this: one with a `Children` field, and one without. (And there may be more in other queries!) Of course, we could name them `User1` and `User2`, but that's both less descriptive and less stable as the query changes (perhaps to add `parent`), so we call them `GetFamilyNamesUser` and `GetFamilyNamesUserChildrenUser`. | ||
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| For the long answer, see [DESIGN.md](DESIGN.md#named-vs-unnamed-types). | ||
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| If you find yourself needing to reference long generated names, you can always add type aliases for them, e.g.: | ||
| ```go | ||
| type User = GetFamilyNamesUser | ||
| type ChildUser = GetFamilyNamesUserChildrenUser | ||
| ``` | ||
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| ### … my editor/IDE plugin not know about the code genqlient just generated? | ||
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| If your tools are backed by [gopls](https://github.com/golang/tools/blob/master/gopls/README.md) (which is most of them), they simply don't know it was updated. In most cases, keeping the generated file (typically `generated.go`) open in the background, and reloading it after each run of `genqlient`, will do the trick. |
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